SEC–MALLS analysis of ethylenediamine-pretreated native celluloses in LiCl/N,N-dimethylacetamide: softwood kraft pulp and highly crystalline bacterial, tunicate, and algal celluloses

Abstract

Softwood and hardwood bleached kraft pulps (SBKP and HBKP, respectively) and highly crystalline native celluloses such as algal, tunicate, bacterial and cotton lint celluloses were dissolved in 8 % (w/v) LiCl/N,N-dimethylacetamide (DMAc) after ethylenediamine (EDA) pretreatment. Complete dissolution of SBKP and other highly crystalline native celluloses in 8 % LiCl/DMAc was achieved after solvent exchange from EDA to DMAc through methanol. Neutral sugar composition analysis showed no significant differences between the original and EDA-treated pulps. A combination of size-exclusion chromatography and multi-angle laser light scattering (SEC–MALLS) was used to analyze the cellulose solutions after dilution to 1 % (w/v) LiCl/DMAc. The 0.05 % (w/v) solutions of highly crystalline cellulose in 1 % (w/v) LiCl/DMAc contained entangled molecules, and therefore 0.025 % (w/v) cellulose solutions in 1 % (w/v) LiCl/DMAc were used in the SEC–MALLS analysis to obtain reliable conformation plots (or double-logarithmic plots of molecular mass vs. root-mean-square radius). All the cellulose samples except SBKP gave conformation plots with slope values of 0.56–0.57, showing that these cellulose molecules had random-coil conformations. In contrast, SBKP gave a slope value of 0.35, indicating that some branched structures were present in the high-molecular-mass fraction. Double-logarithmic plots of the reduced viscosities of the cellulose solutions in 1 % (w/v) LiCl/DMAc versus the molecular mass were linear, except for SBKP, also suggesting the presence of anomalous cellulose structures in SBKP.